In a semiconductor device used in a communication device or the like, a structure in which a package surface is covered by a conductive shield layer is used in order to suppress an electromagnetic interference such as EMI (Electro Magnetic Interference). As a semiconductor device having a shielding function, there is known a structure having a conductive shield layer provided along an upper surface and a side surface of a sealing resin layer which seals a semiconductor chip. In the formation of the conductive shield layer, a plating method, a sputtering method, a coating method of conductive paste, or the like is used. Among the formation methods of the conductive shield layer, the plating method has wet steps such as a pre-treatment step, a plating step, and a water-washing step, so that an increase in a manufacturing cost of a semiconductor device is unavoidable. The coating method of conductive paste also easily causes the increase in a manufacturing cost of the semiconductor device, since it includes a coating step with respect to side surfaces of a sealing resin layer.
The sputtering method includes dry steps, so that it is possible to reduce the number of steps of formation, a formation cost and the like of the conductive shield layer. When the sputtering method is applied to the formation of the conductive shield layer, it is considered to form the conductive shield layer before dividing the semiconductor packages into pieces. In such a case, semiconductor chips are first mounted on respective wiring board regions of a multi-cavity integrated board, and next, the semiconductor chips are collectively resin-sealed. Subsequently, the sealing resin layer and a part of the integrated board are cut to form a half-cut groove. The half-cut groove is formed to make a ground wiring line of the wiring board region to be exposed to a side surface. By sputtering a metal material on the resin-sealed body having the half-cut groove, the conductive shield layer is formed. On side surface of the sealing resin layer and a part of side surface of the wiring board region, the metal material is sputtered via the half-cut groove.
A width of the half-cut groove is limited. Therefore, when the metal material is sputtered via the half-cut groove, there is a possibility that an adjacent package becomes an obstacle, and that the side surface of the sealing resin layer and the wiring board region cannot be sufficiently covered by the conductive shield layer. If the side surface of the sealing resin layer and the wiring board region are covered by the conductive shield layer with a sufficient thickness, the metal material is deposited thickly on an upper surface of the sealing resin layer in which no obstacle exists. This becomes a main cause of increasing the formation cost of the conductive shield layer. Regarding the half-cut of the integrated board with a small thickness, it is difficult to control of a depth of cut, and depending on circumstances, there is a possibility that the semiconductor packages are divided into pieces. From the circumstances as above, when forming the conductive shield layer on the package surface by applying the sputtering method, a technique to forming the conductive shield layer more surely and with a lower cost, is required.